Chert Grains Research Articles

Tectonic Significance of Lithicwacke-Polymictic Conglomerate Petrofacies Association Within Upper Cretaceous Torchlight Sandstone, Big Horn Basin, Wyoming: ABSTRACT

The Torchlight Sandstone belonging to the Upper Cretaceous Frontier Formation in the Big Horn basin, Wyoming, shows a distinctive lithicwacke-polymictic conglomerate is composed of granule-cobble-sized clasts of quartzite, chert, andesite, and argillite, and phyllite. The survival of phyllite, argillite, and neovolcanic andesite clasts indicate that the detritus underwent very little subaerial transport before it was deposited along the proximal margin of the foreland basin. A petrologically heterogeneous upland source of high to moderate relief is indicated by the clast size and composition. Hydrodynamic structures, in conjunction with textural attributes, and compositional data indicate that detritus moved southeast from its source terrane and was deposited by a high-energy distributary complex. The lithicwacke petrofacies is dominated by higher chert and quartz content with a subordinate amount of labile components including paleovolcanic clasts and fine-grained matrix. The development of phyllosilicate matrix around quartz and chert grains preserved the primary porosity and permeability of the sandstone. Absence of any noticeable quartz overgrowth apparently contributed to the preservation of good reservoir quality in this petrofacies. Considering its (Torchlight Sandstone) close proximity to the thrust belt and to the locus of andesite volcanism in the northwest and west, it is suggested that the extrabasinal detritus withinmore » the foreland basin can provide significant clues as to the timing of the thrust events and volcanicity in the adjacent region. New perspectives for hydrocarbon exploration and regional correlation may be gained by employing this petrofacies association.« less

Fluvial origin of the lower Proterozoic Sioux Quartzite, southwestern Minnesota

The Sioux (Quartzite of inferred Early Proterozoic age (1,760−1,630 m.y.) occurs in southwestern Minnesota, eastern South Dakota, and adjoining parts of Iowa and Nebraska where it overlies a regolith developed on an older Precambrian crystalline basement. The rocks constitute a red-bed sequence that was deposited by braided streams flowing over a deeply weathered land surface of moderate relief. Deposition was confined largely to fault-bounded basins in a cratonic setting; the basins subsided slowly and were rarely, if ever, areas of steep relief. The Sioux Quartzite is a texturally and mineralogically mature quartz arenite. Sand grains are mainly monocrystalline quartz with rare grains of chert, granular iron-formation, and quartzite. Scattered conglomeratic layers contain lithic clasts that include red quartzite, chert, iron-formation, vein quartz, and rhyolite, together with rare welded rhyolite tuff and granitoid gneiss. Stratigraphic intervals of conglomeratic orthoquartzite are interspersed throughout the basal two-thirds of the formation, whereas thin units of sericitic mudstone are most abundant in the upper third. Overall, the upward fining of size grades in the Sioux may indicate diminishing stream gradients and reduction of relief in source areas during deposition. The diagenetic minerals diaspore, kaolinite, and quartz cement indicate an environment of intense leaching, probably under warm, humid climatic conditions, during or closely following deposition. Detrital feldspar, present in trace amounts in deeper parts of the stratigraphic section, may have been more abundant originally but was destroyed by intrastratal reactions. The sub-Sioux regolith is characterized by (1) fine-grained kaolinite and sericite formed from intensively altered coarse-grained metamorphic feldspar and (2) the presence of abundant secondary hematite and silica. By virtue of its Early Proterozoic age, its alluvial origin, and its unconformable position above older Proterozoic and Archean rocks, the Sioux is inferred to have some potential for unconformity-related, Athabasca-type uranium deposits. Its provenance, which includes older Proterozoic iron-formation and volcanic rocks (greenstone), enhances its potential for paleoplacer gold deposits.

Provenance and Diagenesis of Ivishak Sandstone, Northern Alaska: ABSTRACT

The Ivishak sandstone of northern Alaska is a regressive sequence of Lower Triassic fluvial and paralic deposits that constitutes an important hydrocarbon reservoir in the Prudhoe Bay area. A petrographic study of the formation, utilizing samples from wells from both reservoir and non-reservoir rocks, was undertaken to determine the provenance and diagenetic histories of the formation. The Ivishak sandstone can be characterized as a low-rank or lithic graywacke. The major detrital species it contains include: (a) quartz (46%), dominantly reworked sedimentary and volcanic monocrystalline quartz and metamorphic polycrystalline quartz; (b) chert (22%), containing variable amounts of inclusions (clay and carbonate); (c) sedimentary rock fragments (10%), largely mudstones and silty mudstones; and (d) metamorphic End_Page 504------------------------------ rock fragments (4%), mostly slate and phyllite. Feldspars are conspicuously absent in the sandstone. This detrital suite, and the overall decrease to the southwest in the grain size of the sandstone, indicate that the sands of the formation were derived from a northern landmass, exposed in the Late Permian and Early Triassic, which consisted of Precambrian schists and quartzites overlain by early Paleozoic marine sandstones and deep-water cherts and argillites. After deposition, the reservoir facies of the Ivishak sandstone underwent 4 consecutive diagenetic phases: (1) early carbonate cementation that prevented mechanical compaction, (2) dissolution of pore-filling carbonate and carbonate inclusions within chert grains, (3) precipitation of quartz as overgrowths, and (4) precipitation of authigenic kaolinite. At present, the intergranular porosity of the formation is high, averaging 11.5%, and is present in the forms of elongate and oversized secondary pores. Porosity also occurs as micropores associated with leached chert grains and with the kaolinite. In the more matrix-rich nonreservoir facies of the Ivishak, the clay matrix prevented complete carbonate cementation which allowed for greater mechanical compaction of the sandstones; in som places, this mechanical compaction, coupled with the precipitation of quartz overgrowths, reduced porosity to irreducible levels. End_of_Article - Last_Page 505------------

Compaction in Sandstones--Influence on Reservoir Quality: ABSTRACT

Primary porosity that is lost during burial through cementation by carbonate, evaporite, and some clay minerals can be regenerated during the stage of secondary porosity development that is typical of most basins. However, primary porosity that is lost through compaction is forever lost and cannot be regenerated. Thus, it is desirable to be able to predict the amount of porosity loss expected in sandstones buried to given depths. During progressive burial, terrigenous sandstones compact by (1) packing readjustments without changes in grain shape, (2) ductile deformation of clayey and micaceous grains, chiefly rip-up-clasts, fecal pellets, and fragments of shale, mudstone, slate, and schist, (3) bending of flexible micas, (4) pressure solution, and (5) fracturing of feldspar, quartz, and chert grains. Process 1 generally results in a 7-10% porosity loss and is independent of sandstone composition; processes 2, 3, and 4 are strongly dependent on framework composition and each by itself is responsible for producing tight sandstones; and process 5 is generally not important. Process 3 was modeled by Rittenhouse, who showed that sandstones with 35% ductile grains can compact to produce tight sandstones. Pressure solution becomes important at depths greater than 8,000 ft (2,400 m). Pressure solution at quartz grain contacts is enhanced where thick illite or chlorite clay coats develop and is most common in quartz-rich sandstones that lack much quartz cement. Quartz dissolved from grains generally exits the formation instead of being precipitated as cement. Stylolites develop at mica-rich and clay-rich laminae and develop conspicuous vertical permeability barriers. Wholesale dissolution of quartz grains leaves a residue of clay, micas, organic matter, and feldspar. End_of_Article - Last_Page 505------------

Sedimentology and Depositional Environments of Emery Sandstone, Emery and Sevier Counties, Utah: ABSTRACT

From a sedimentologic study of the Emery Sandstone Member of the Mancos Shale (Upper Cretaceous) in southern Castle Valley, Utah, it is possible to determine depositional environments, paleogeography, textural and mineralogical characteristics, and possible sediment sources. Tidal-flat deposits are dominant in the Emery, but subtidal (shoreface) and offshore deposits also occur. The paleotidal range is estimated to have been 1.3-1.7 m (4.3-5.6 ft). Many asymmetric, transgressive-regressive cycles of two different magnitudes and periods are present. They formed in response to minor fluctuations in sea level combined with slight variations in the subsidence rate. The Emery Sandstone was deposited in the foreland of the Sevier orogenic belt. The average orientation of the paleoshoreline, as determined by paleocurrent analysis, was N9°W. Sediment was probably transported southward from the Utah-Idaho-Wyoming border area by longshore currents. Well-sorted, subrounded to subangular, very fine-grained subarkose is the dominant rock type in the Emery. Dolomite and calcite are the major cements. Average porosities, based on thin section analysis, are less than 2%. Abundant chert grains and reworked authigenic quartz overgrowths suggest a sedimentary source terrane. The observed amounts of feldspar could have been derived from Mesozoic sedimentary rocks exposed in the Sevier orogenic belt. End_of_Article - Last_Page 942------------

Jurassic Subcrop and Its Effect on Sedimentation, West-Central Alberta: ABSTRACT

In eastern and central Alberta, topography on the Pre-Cretaceous surface reflects the presence of a northwest-trending drainage system which intermittently carved into older Paleozoic rocks from Late Mississippian until earliest Cretaceous time. Lower Cretaceous sedimentary rocks mapped across the area fill and cover the valley and ridge system. To the west, successively younger units subcrop at the Pre-Cretaceous surface. As a result, unconformity bounded Jurassic quartz sandstones are present beneath Cretaceous sandstones and, in the absence of paleontologic control (usual situation), can only be distinguished with difficulty. The tendency has been to include these sands in the Lower Cretaceous Basal Quartz, masking the unconformity surface. Subsequent interpretation f Lower Cretaceous sedimentation patterns is seriously affected. Mineralogically pure, fine-grained quartz sandstones of the Rock Creek Member (Middle Jurassic) in west-central Alberta are distinct from quartz sandstones of Early Cretaceous age, which have greater grain-size variation and significantly higher percentages of unweathered chert grains. The resulting Jurassic subcrop pattern reveals cuestas of resistant Rock Creek sandstone, similar to those composed of Mississippian carbonates farther east. Erosional lows on the surface of the Rock Creek Member are commonly filled by estuarine and nearshore sediments of the Ellerslie Member, reflecting invasion of the Early Cretaceous sea into the sea. End_of_Article - Last_Page 599------------

Origin of Chert Grains and a Halite-silcrete Bed in the Cambrian and Ordovician Whitehall Formation of Eastern New York State

ABSTRACT A chert bed in the Whitehall Formation (Cambrian and Ordovician) of eastern New York State is strikingly similar in petrography and inferred origin to Australian and South African silcretes. The chert in the Whitehall, like its Australian and South African counterparts, occurs along an erosion surface that formed subarially, and it contains colloform chalcedony and abundant ferruginous minerals. This chert also contains pseudomorphs and ghosts of halite. Silica precipitated from a solution that became enriched in electrolytes as a result of dissolving halite. Sand-size chert grains in the Whitehall are petrographically like the Whitehall silcrete and are probably grains of reworked silcrete.

Sedimentology of Fluvial Upper Devonian Kanayut Conglomerate, Brooks Range, Alaska: ABSTRACT

The Kanayut Conglomerate, which extends across most of the Brooks Range in northern Alaska, is a widespread nonmarine clastic sequence as thick as 2,000 m. It records southwestward growth of a major fluvial-dominated coarse-grained delta. The Kanayut is underlain and overlain by fossiliferous marine strata of the Upper Devonian Hunt Fork Shale and Lower Mississippian Kayak Shale, respectively. It has been subdivided into four members, in ascending order: (1) a lower marine member, 560 m thick, consisting chiefly of sandstone; (2) a lower nonmarine member, 550 m thick, consisting chiefly of fining-upward cycles of sandstone to shale; (3) a middle nonmarine member, 450 m thick, consisting of massive interbedded conglomerate and sandstone; and (4) an upper nonmarine member, he Stuver Member, 400 m thick, consisting chiefly of fining-upward cycles of sandstone to shale. The distribution of maximum size of conglomerate clasts suggests a source area to the northeast, and paleocurrent measurements indicate sediment transport dominantly toward the southwest. The conglomerates are texturally and compositionally mature, containing primarily clasts of chert with lesser amounts of quartz, quartzite, and argillite. The sandstones are also compositionally and texturally mature, composed chiefly of subrounded grains of quartz, chert, and argillite, with negligible amounts of feldspar. The Hunt Fork Shale, Kanayut Conglomerate, and Kayak Shale record a major progradational-retrogradational deltaic cycle. The lower marine member of the Kanayut and underlying and overlying marine units represent prodelta, delta-margin, and delta-front deposits, the lower nonmarine member and the Stuver Member of the Kanayut represents meandering fluvial delta-plain deposits, and the middle nonmarine member of the Kanayut represents braided fluvial delta-plain deposits. End_of_Article - Last_Page 758------------

North Cross (Devonian) Unit CO2 Flood - Review of Flood Performance and Numerical Simulation Model

Although the North Cross (Devonian) Unit CO2 flood has not performed as dramatically as predicted, response to CO2 injection has been encouraging. Sharp, sustained production increases in responding wells and minimal CO2 breakthrough indicate that CO2 is displacing oil efficiently. No major operating problems have been encountered so far. CO2 injectivities have been significantly below initial predictions. Introduction The Crossett Field (Crane and Upton counties, west Texas) was discovered in 1944 with the Texaco Hobbs A-1 well. Development of the 28-well field essentially was completed by the mid-1950's. The major producing horizon is the Devonian "Main Pay," a classical Archie Type 11-A rock composed of microscopic, tripolitic chert grains bound by limestone cement. The formation is characterized by high porosity, averaging 22%, and low uniform permeability, averaging 5 md. Connate water saturation averages 35%. The Crossett Devonian is a stratigraphic trap, bounded on the north, south, and west flanks by a deterioration of porosity, and on the east flank by the producing water porosity, and on the east flank by the producing water level of - 3,040 ft (Fig. 1). The reservoir oil was initially saturated (PVT properties are presented in Table 1), and a gas-oil contact existed at -2,860 ft. The gross pay distribution is described in Fig. 2. Net-to-gross pay ratios for individual wells range from 70 to 100%, and pay continuity among wells is very good. The primary producing mechanism of solution gas drive ultimately will recover 12.9% of the original oil in place. The field was developed on regular 40-acre spacing and produced under primary recovery until 1964. Crossett Field was unitized in 1964, when the North Cross (Devonian) Unit (operated by Shell Oil Co. with a working interest of 58.3%) was formed. Simultaneously, a program of partial pressure maintenance by updip program of partial pressure maintenance by updip residue-gas injection began. That program added 45% of the field's ultimate recovery to its recoverable reserves. Waterflooding is not feasible because of the reservoir's extremely low permeability to water; various other means of enhanced recovery were studied. Of these, miscible displacement by CO2 injection was the most attractive. When a CO2 source became available in 1970, a comprehensive CO2-flood design began. Initial Flood Design Implementation A leasing agreement was signed between Shell and Canyon Reef Carriers (CRC), operator of the SACROC CO2 pipeline, whereby up to 20 MMcf/D of that system's capacity would be made available for CO2 transport to North Cross Unit. The CO2 was to be supplied from Shell's production in the JM and East Brown Bassett gas fields. The 20 MMcf/D (93% CO2, 7% methane) was to be delivered over a 10-year period and would constitute an ultimate solvent slug of 73 Bcf (about 40% of an oil-column hydrocarbon pore volume). Shell's miscible reservoir simulator was used to try to define an optimum flood plan. The field's past production performance was history matched, and project production performance was history matched, and project predictions for several injection patterns and operating predictions for several injection patterns and operating policies were generated and compared. An inverted policies were generated and compared. An inverted nine-spot pattern was found optimal. Wells 46 and 62 were converted to CO2 injection initially, with Wells 44 and 64 to be converted after 4 years of flooding. Continuous solvent injection with recycling was planned. JPT P. 1706

A Review of Waterflood Performance in Garrington Cardium A and B Pools, Unit No. 2

This paper presents the evaluation and prediction of ultimate oil recovery after a petrophysical study of Garrington Cardium A and B pools. Reservoir sands are discussed in detail and waterflood performance is emphasized. Surfactant treatment to improve oil production is described. Introduction The Garrington Upper Cretaceous Cardium field is located about 60 miles northwest of Calgary (Fig. 1) and has two pools, upper Cardium A and lower Cardium B sandstones, separated by about 100 ft of shale. Both sands trend northwest-southeast. Sand A trends for 36 miles with a producing width of about 6 miles. Sand B trends for 42 miles with a maximum width of 1 1/2 miles (Fig. 1). Thicknesses vary, but the maximum is about 20 ft in both pools. The field was discovered in 1954 and waterflood operations began in 1965. This field has four units, but this study discusses only the geology and waterflood performance of Unit 2 (Fig. 1). Knowledge of the origin and performance of Unit 2 (Fig. 1). Knowledge of the origin and postdepositional history of these sands leads to a better postdepositional history of these sands leads to a better understanding of the waterflood performance. Basic rock types were determined by examining detailed cores, measuring mercury-injected capillary pressure, and scanning electron microscope. Rocks were pressure, and scanning electron microscope. Rocks were classified as "good" or "poor" in terms of reservoir potential. Significant differences in the production and potential. Significant differences in the production and waterflood history of Sands A and B can be related to their geological characteristics. Geology Cardium A sand correlates with the producing sand of Pembina field 60 miles northwest. However, it is thinner Pembina field 60 miles northwest. However, it is thinner with poorly developed, clean sand beds. The most distinctive feature of Sand A is the extensive mottling caused by burrowing organisms that mixed sand, silt, and mud together. This action greatly reduced the effective porosity and, particularly, the permeability of the sand; porosity and, particularly, the permeability of the sand; but, more importantly, it destroyed much of the lateral continuity of the sand beds. Thinly laminated, well sorted, clean, fine-grained sandstones are seldom more than 1 to 2 in. thick. Sandstones are composed mostly of quartz and lesser chert grains, with only minor amounts of feldspar, mica, and rare glauconite. X-ray diffraction analysis shows that the dominant clay minerals are illite, chlorite, and kaolinite, with traces of montmorillonite. The kaolinite is well crystallized and probably of diagenetic origin. At the top of the Sand A sequence, there is usually a conglomerate bed that varies from 1 in. to nearly 3 ft thick. This is composed of well rounded chert, quartz, and argillite pebbles embedded in a dense shale matrix. Although nonporous, the conglomerate has well developed, vertical fractures. Laterally, Sand A grades into siltstones and silty shale. Textures and structures indicate that Sand A was deposited in a shoreface environment. Comparison of this conglomerate with that at Pembina and elsewhere indicates that the beds formed as bars on top of an offshore shoal, possibly as a terrace bar, as suggested by Swagor et al. for Cardium conglomerate at Carrot Creek. Sand B is different both in distribution and mineralogy. Its most striking feature is the length of its body relative to width. JPT P. 869

Quartz, Chert, and Feldspars in Modern Fluvial Muds and Sands

ABSTRACT Twenty interbedded fluvial muds and sands (mud-sand pairs) from various rivers in Oklahoma, Missouri, Arkansas, Louisiana, Mississippi and Texas were collected and analyzed. Chemical treatments were used to isolate the solid silica (quartz plus chert) and feldspar from the sediments and point counts of grain mounts were made to determine the amounts of quartz, chert and types of feldspars in each sample. Atomic absorption spectrophotometry was used to obtain normative percentages of orthoclase, albite and anorthite. A combination of sieving and settling tube techniques was used to obtain the size distribution of solid silica plus feldspar fraction of each sample. In the samples analyzed, feldspar is finer grained than quartz plus chert and, therefore, the F/Q + C + F ratio in a mud is higher than the ratio in the associated sand. Consideration of a single size fraction (4.0-4.5 ) common to both the mud and sand members of the mud-sand pairs eliminated the influence of size on the ratio. Within the 4.0-4.5 size fraction the F/Q + C + F ratios for the mud and sand of a mud-sand pair are the same. The chert grains in our chert-rich samples are coarser-grained than the associated quartz grains so that the chert/solid silica ratios are larger in the sands than in the muds. However, as with the feldspar grains the ratios are the same if only the 4.0-4.5 size fraction of each sediment is considered. Most sandstones and almost all mudrocks contain sediment in the 4.0-4.5 size fraction and this study has established that the F/F + Q + C and C/Q + C ratios in this size fraction are the same in these two types of sediments at the time of deposition. This establishes a baseline against which the feldspar, quartz, and chert contents of ancient rocks can be compared to determine, for example, whether feldspar has been preferentially removed from sandstones during diagenesis; or whether authigenic chert has been formed in mudrocks.

Trace Metal Relationships in Bottom Sediments of a Fresh Water Stream--The Buffalo River, Arkansas

ABSTRACT Sediments were sampled over 130 mi of the Buffalo River in northern Arkansas. Aqua regia extracts of the minus 95 mesh fraction of the sediments were analyzed by atomic absorption for Na, K, Mg, Ca, Zn, Cd, Cu, Pb, Fe, Co, Cr, Ni, and Mn. Zirconium was determined by X-ray fluorescence. There was a general decrease downstream in Fe, Cu, Cr, Ni, Mn, Pb, K, and Na as the drainage area increased in carbonate rock and decreased in shale. The elements Mg, Ca, Zn, and Cd increased in sediments downstream. The sediments are mainly quartz and chert grains. These grains are apparently coated with hydrous iron oxide which acts as a sorbent for most of the metals and is a dominant transport mechanism for acid extractable Co, Cr, Ni, Cu, Mn, and K. Other acid extractable metals, particularly Mg, Ca, Zn, Cd, and Pb are mostly in clastic grains. Cadmium to zinc ratios in the sediments and in ore minerals of the area are similar. The ore metals of the drainage area are Zn, Pb, and Cu. The acid extractable amounts of these metals in the sediments rise and fall with the extractable amounts of Ca plus Mg in the sediments, indicative of the favorite host rock, dolomite. Tributaries are sites of rapid rise and fall of metal values within a few miles from background to anomalously high values and return to background.

Differential Cementation of a Pleistocene Carbonate Fanglomerate, Guadalupe Mountains

Pleistocene fanglomerates, extending southeastward from the Guadalupe Mountains, consist of predominantly micritic carbonate particles (limestone and dolostone) eroded from the Permian reef complex. Accessory particles consist of detrital monocrystalline grains of calcispar, quartz and chert. The fanglomerate is firmly cemented by low-magnesium calcite which was precipitated in the vadose zone. Predominantly micritic particles are coated by bilaminar films, consisting of an inner calcimicrite lamina and an outer rim of drusy, dogtooth spar. Bilaminar films do not completely occlude porosity in large neighboring interstices. Monocrystalline carbonate grains are concentrated in the sand-size fraction and are enveloped by thin, discontinuous micrite films and thick overgrowth aureoles which expand outward to occlude porosity in adjacent interstices. The following lines of evidence suggest that overgrowth aureoles on monocrystalline grains were precipitated at much greater rates than outer drusy rims of bilaminar film-coated grains: (1) both monocrystalline grains and bilaminar film-coated grains are enveloped by thin, inner micrite films, suggesting that outer drusy films are homologous with overgrowth aureoles; (2) overgrowth halos on monocrystalline grains are 3-10 times thicker than outer drusy rims of dogtooth spar on similar-sized bilaminar film-coated particles; (3) where overgrowth aureoles expand outward and engulf neighboring grains, growth of outer drusy rims is poorly developed or commonly precluded. Bilaminar films, especially outer drusy rims, commonly exhibit gravitational cementation, recording precipitation in pendulous vadose water films.

Source and Depositional Environments of the Moose Channel Formation, Northwest Territories

ABSTRACT The Moose Channel Formation of the Fish River area, Northwest Territories, comprises over 8200 ft of clastic rocks. The strata, of Maestrichtian-Paleocene age, are genetically equivalent to much of the thick clastic section underlying the Mackenzie Delta. The sandstones in the Moose Channel Formation are mineralogically and texturally immature. An abundance of feldspars, chert grains, and sedimentary and volcanic rock fragments indicates granitic, sedimentary and volcanic source terranes. The Old Crow granites and the volcanic rocks of the British Mountains are possible sources of the igneous clasts. Many of the sedimentary rock fragments are assumed to have been derived from the Richardson Mountains south of the study area. Paleocurrent measurements show that northerly and easterly transport directions prevailed during deposition of the Moose Channel clastics. Grain-size analyses of 125 sandstone samples indicate that unidirectional current energy and gravitational energy were the two basic kinds of energy responsible for deposition of most of the sandstones. These two energy types are compatible with fluvial depositional processes. The Moose Channel Formation has been divided into five units after Young (1971, 1972). The depositional environment of each unit has been interpreted as follows: Unit 1, the oldest, is a regressive sequence containing prodelta and braided-stream deposits. Unit 2, a transgressive sequence, contains prodelta deposits grading upwards into nearshore marine silty shale and fine-grained sandstone. Unit 3, dominantly sandstone, is interpreted as fluvial deposits. Unit 4 is interpreted as a transitional marine-nonmarine delta-plain complex. The youngest strata, in Unit 5, are interpreted as nearsource channel and overbank deposits. An analogy is drawn between the depositional settings of these units and those of the Wilcox Group of Texas (Fisher and McGowen, 1969).

Late Cretaceous Age of Strata Mapped as “?Matilija Formation” (Late Eocene), Lompoc Quadrangle, Santa Barbara County, California

Strata mapped as “?Matilija Formation” (late Eocene) by Dibblee (1950) are Late Cretaceous in age and in actuality represent the Jalama Formation. Calcareous nannoplankton and benthonic foraminifers indicate a late Campanian–early Maastrichtian age, equivalent to the Tetralithus trifidus zone (nannoplankton). A “Franciscan” terrain provenance for these sediments is indicated by the presence of grains of red and black chert and serpentinite.

Differential Cementation of Pleistocene Carbonate Fanglomerate, Guadalupe Mountains: ABSTRACT

Pleistocene fanglomerates, extending southeastward from the Guadalupe Mountains, consist of predominantly micritic carbonate particles (limestone and dolostone) eroded from the Permian reef complex. Accessory particles consist of detrital monocrystalline grains of calcispar, quartz, and chert. The fanglomerate is firmly cemented by low-magnesium calcite. The fanglomerate was cemented in the vadose zone. Predominantly micritic particles are coated by bilaminar films, consisting of inner calcimicrite laminae and outer rims of drusy, dogtooth spar. Bilaminar films do not completely occlude porosity in large neighboring interstices. Monocrystalline carbonate grains are concentrated in the sand-size fraction and are enveloped by thin, discontinuous micrite films and thick over rowth aureoles which expand outward to occlude porosity in adjacent interstices. The following lines of evidence suggest that overgrowth aureoles on monocrystalline grains were precipitated at much greater rates than outer drusy rims of bilaminar film-coated grains: (1) both monocrystalline grains and bilaminar film-coated grains are enveloped by thin inner micrite films, suggesting that outer drusy rims are homologous with overgrowth halos; (2) overgrowth rims on monocrystalline grains are 3-10 times thicker than outer rims of dogtooth spar on similar-sized, bilaminar film-coated particles; (3) where overgrowth halos expand outward and engulf neighboring grains, outer drusy rims are missing or poorly developed. Bilaminar films, especially outer drusy rims, thicken downward from lower grain boundaries into interstices in response to a gravitational effect (downward thickening of water films). End_of_Article - Last_Page 786------------

Petrography of fine aggregates from Kaligandaki River, western Nepal: implication for assessment of deleterious constituents

Seven fine aggregate samples from test pits driven at the river banks of the Kaligandaki River and banks of the contributingstreams around Kokethanti-Chhyo Bagar area were petrographically analysed as these will be used for concrete aggregates. Theaggregates had median grains size of 0.45-1.00 mm and were well graded. They were dominantly composed of carbonate rockfragments and the total QFL modes being Q14.81–28.87F0.63–4.58L66.55–84.15. All the samples were classified as medium-grainedcalc-lithic sands. Quartz grains were dominantly megaquartz. Some chert grains and few quartz grains occurring in siliceouslimestones were of microquartz.Considering deletereous constituents, the sample T1 had chert fragments. The sample T2 had high amount of micas suggestingits low workability. Silt/clay-grade size fraction was the deletereous material to all the samples and this fraction should be removedduring processing. The samples T2, T6 and T7 showed greater preferability among the samples as these had lower amount ofunsound rock fragments such as carbonaceous schists/phyllite, and other deletereous materials.DOI: http://dx.doi.org/10.3126/bdg.v14i0.5436Bulletin of the Department of Geology Vol.14 2011, pp. 29-34

Pleistocene, Holocene and Recent Bird Gastroliths from Interior Alaska

Describes and discusses the origin of polished and rounded grains of quartz, secondary quartz, and chert from (probably) Holocene loess of Easter Egg Hill near Livengood townsite, peat on the Nenana Road, and redeposited Wisconsin loess from the Eva Creek Mine and Ready Bullion Creek Mine at 64 51 N, 148 02 W. The association of these grains with dull, angular grains of the same materials rules out soil or solifluction abrasion in place. Gizzard-bearing birds such as ptarmigan and grouse in Alaska produce glossy polish on their gizzard stones (gastroliths) comparable to that of the Pleistocene and Holocene gastroliths; the polish and roundness of the stones in living birds are more pronounced in late winter. Because the modal size classes of ancient and Recent polished gastroliths do not coincide, some of the ancient gastroliths are believed to have been produced by birds not now living in interior Alaska.

Stratigraphy and Origin of Maravillas Formation (Upper Ordovician), West Texas

The Maravillas Formation is a distinctive chert-rich formation that was deposited in deep water on the slope and floor of the Ouachita geosyncline in West Texas. It is 40 percent black chert; 30 percent fetid calcarenite, micrite, and marlstone; 14 percent shale; 10 percent chert of other colors; 5 percent limestone-pebble conglomerate; and 1 percent dolomite. These rocks are intercalated in even beds, generally 3-12 in. thick. The formation ranges from 60 to almost 500 ft in thickness; isopach lines delineate a lens-shaped body whose axis (uncorrected palinspastically) is northeast-southwest and is parallel with tectonic strike. In the Marathon basin the formation is divided, from bottom to top, into three members: (1) limestone and chert, (2) chert and limestone, and (3) chert and shale. Members 1 and 2 differ chiefly in that limestone predominates in member 1 and chert predominates in member 2. In many places member 2 can be divided into three units. Member 3 is predominantly shale at the southern and eastern margins of exposures, and is the Solitario Formation of Baker and the Persimmon Gap Formation of Wilson. Calcarenite beds are composed of skeletal grains, intraclasts, pellets, and minor shale, chert, quartz, phosphate, and glauconite grains. Laminated, or graded and laminated, beds predominate. Micrite and marlstone are composed of compacted pelletal(?) and clayey pelletal(?) silt and mud. Conglomerate beds are composed of limestone and chert clasts derived from shelf equivalents of the Maravillas and older formations. Paleocurrent data and grain-size trends indicate that detritus was derived from the northwest. Calcarenite was deposited largely by turbidity currents; conglomerate was laid by turbidity currents, debris flows, and possibly nonturbid density currents; and micrite, marl, and clay settled as a rain of sediment from weak geostrophic or nonturbid density currents. The geometry and relict texture of chert lenses and beds prove that most chert is of replacement origin, but a few beds are altered siliceous ooze. Lumpy and chalcedony-veined black chert beds in member 2 formed as submarine slide deposits. The preservation of abundant organic material (3.7 percent organic carbon), including some petroleum, in some beds and the absence of bioturbation features indicated that sedimentation generally occurred in an euxinic environment. The grain size in the formation is generally coarser at the bottom and finer at the top, a response to a major epeirogenic pulse that affected the shelf northwest of the geosyncline. Deposition of clay and spiculitic clay continued after the influx of carbonate had ceased.

Mineralogy and origin of the upper Eastend and Whitemud Formations of south-central and southwestern Saskatchewan and southeastern Alberta

The Upper Cretaceous non-marine Whitemud Formation of south-central and southwestern Saskatchewan and southeastern Alberta consists of kaolinitic, metamorphic lithic sands and silts, and kaolinitic clays. The sands and silts are not highly feldspathic as was originally thought. The major constituent is metamorphic lithic grains with minor kaolinitic clay and vermicular kaolin, clear angular quartz, chert, muscovite, and minor volcanic lithic grains and feldspar. The upper part of the Upper Cretaceous Eastend Formation, which conformably underlies the Whitemud Formation, consists of nonmarine sands, silts, and clays. Kaolin is very rare. The bulk of the sands are composed of volcanic lithic grains with minor metamorphic lithic grains, clear angular quartz, chert, feldspar, muscovite, and biotite. The contact is characterized by the following changes from the Eastend Formation upward into the Whitemud Formation: an abrupt decrease in volcanic lithic grains and increase in metamorphic lithic grains; the appearance of kaolin and the disappearance of biotite and apatite; a slight increase in clear angular quartz and muscovite and a decrease in feldspar; a general increase in metamorphic heavy minerals; and an increase in the percentage of ilmenite (both as solitary grains and intergrown with magnetite), which is altered to leucoxene. On the basis of mineralogy, the Whitemud Formation is definitely a correlative of the Colgate Member of the Fox Hills Formation in Montana and North Dakota. The upper Eastend and Whitemud Formations were derived from Upper Cretaceous volcanic rocks, Precambrian and Paleozoic metamorphic rocks, and Paleozoic carbonates all situated in Montana. Upper Eastend sediments represent fast mechanical weathering of mountains of freshly extruded volcanic rocks, whereas the Whitemud sediments represent slow chemical weathering and leaching, which predominated once the mountainous volcanic rocks were worn down. This deep chemical weathering altered the volcanic tuffs and flows into kaolinitic clay at the source area; the kaolin of the Whitemud Formation is not derived from the weathering of feldspars at the site of deposition. It is suggested that the Frenchman and Ravenscrag Formations were also derived from Upper Cretaceous and Lower Tertiary volcanic rocks in Montana.